U.S. patent application number 12/959021 was filed with the patent office on 2011-03-31 for method for producing core-shell particles, core-shell particles, method for producing hollow particles, coating composition and article.
This patent application is currently assigned to ASAHI GLASS COMPANY, LIMITED. Invention is credited to Yohei KAWAI, Takashige Yoneda.
Application Number | 20110076484 12/959021 |
Document ID | / |
Family ID | 41398170 |
Filed Date | 2011-03-31 |
United States Patent
Application |
20110076484 |
Kind Code |
A1 |
KAWAI; Yohei ; et
al. |
March 31, 2011 |
METHOD FOR PRODUCING CORE-SHELL PARTICLES, CORE-SHELL PARTICLES,
METHOD FOR PRODUCING HOLLOW PARTICLES, COATING COMPOSITION AND
ARTICLE
Abstract
To provide a method whereby core-shell particles and hollow
particles can be produced while suppressing formation of a gel or
particles made of a shell-forming material; core-shell particles
and a coating composition wherein a shell thickness is strictly
controlled; and an article having a coating film having a high
antireflection effect. Core-shell particles obtained by irradiating
a liquid containing core particles made of a material having a
dielectric constant of at least 10 and a metal oxide precursor with
a microwave to form a shell made of a metal oxide on the surface of
the core particles are used.
Inventors: |
KAWAI; Yohei; (Tokyo,
JP) ; Yoneda; Takashige; (Tokyo, JP) |
Assignee: |
ASAHI GLASS COMPANY,
LIMITED
Tokyo
JP
|
Family ID: |
41398170 |
Appl. No.: |
12/959021 |
Filed: |
December 2, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/JP09/60193 |
Jun 3, 2009 |
|
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|
12959021 |
|
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Current U.S.
Class: |
428/328 ;
106/286.6; 427/595 |
Current CPC
Class: |
C09C 1/043 20130101;
Y10T 428/256 20150115; C01P 2004/64 20130101; C09C 1/3661 20130101;
C09D 7/62 20180101; C01P 2004/84 20130101; C01P 2002/52 20130101;
B82Y 40/00 20130101; C01B 13/145 20130101; C09C 1/3054 20130101;
C09D 5/006 20130101; C09D 7/67 20180101; B82Y 30/00 20130101; C09D
7/70 20180101; C01G 19/02 20130101; C01G 23/047 20130101; C08K 3/22
20130101; C01P 2006/40 20130101; C09C 3/063 20130101; C09D 7/42
20180101; C01G 9/02 20130101; C09D 7/68 20180101; C01P 2004/34
20130101; B01J 19/126 20130101 |
Class at
Publication: |
428/328 ;
427/595; 106/286.6 |
International
Class: |
B32B 5/16 20060101
B32B005/16; C23C 14/00 20060101 C23C014/00; C09D 1/00 20060101
C09D001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 3, 2008 |
JP |
2008-145490 |
Claims
1. A method for producing core-shell particles, which comprises
irradiating a liquid containing core particles made of a material
having a dielectric constant of at least 10 and a metal oxide
precursor with a microwave to form a shell made of a metal oxide on
the surface of the core particles.
2. The method for producing core-shell particles according to claim
1, wherein the core particles are zinc oxide particles, titanium
oxide particles, or particles of tin oxide doped with indium.
3. The method for producing core-shell particles according to claim
1, wherein the metal oxide precursor is an alkoxysilane.
4. The method for producing core-shell particles according to claim
1, wherein the output power of the microwave is an output power by
which the liquid containing core particles made of a material
having a dielectric constant of at least 10 and a metal oxide
precursor, is heated to a level of from 30 to 500.degree. C.
5. The method for producing core-shell particles according to claim
1, wherein the core particles have an average agglomerated particle
size of from 1 to 1,000 nm.
6. The method for producing core-shell particles according to claim
1, wherein the shell of the core-shell particles has a thickness of
from 1 to 500 nm.
7. The method for producing core-shell particles according to claim
1, wherein the core-shell particles have an average agglomerated
particle size of from 3 to 1,000 nm.
8. Core-shell particles prepared by the production method as
defined in claim 1.
9. A method for producing hollow particles, which comprises
dissolving or decomposing the core particles of the core-shell
particles prepared by the production method as defined in claim
1.
10. The method for producing hollow particles according to claim 9,
wherein the core particles are zinc oxide particles.
11. The method for producing hollow particles according to claim 9,
wherein the metal oxide precursor is an alkoxysilane.
12. A coating composition comprising the hollow particles prepared
by the production method as defined in claim 9, and a dispersion
medium.
13. An article comprising a substrate and a coating film made of
the coating composition as defined in claim 12 formed on the
substrate.
14. The article according to claim 13, wherein the coating film has
a refractive index of from 0.0 to 1.4%.
Description
TECHNICAL FIELD
[0001] The present invention relates to a method for producing
core-shell particles, core-shell particles prepared by the
production method, a method for producing hollow particles using
the core-shell particles, a coating composition comprising hollow
particles prepared by the production method and an article
comprising a coating film made of the coating composition.
BACKGROUND ART
[0002] Metal oxide particles such as titanium oxide and zinc oxide
particles have ultraviolet shielding properties, and they are used
as resin fillers, cosmetics, etc. Further, metal oxide particles
such as particles of tin oxide doped with indium (hereinafter
referred to as ITO) have infrared shielding properties, and they
are used as fillers for resin, coatings for glass, etc.
[0003] However, such metal oxide particles have the following
problems.
[0004] (i) Titanium oxide, zinc oxide, etc. have a photocatalytic
activity, and in a case where such metal oxide particles are used
for fillers for resin, cosmetics, etc., they are likely to
decompose organic matters (other components composing resin or
cosmetics).
[0005] (ii) In a case where zinc oxide particles are used for
fillers for fluororesin, zinc oxide reacts with fluorine compounds
released from a fluororesin, causing zinc fluoride to be
deteriorated. Therefore the ultraviolet shielding properties are
weakened.
[0006] (iii) In a case where ITO particles are used for fillers for
resin, coatings for glass, etc., ITO deteriorates due to oxidation.
Therefore the infrared shielding properties are weakened.
[0007] Accordingly, in a case where metal oxide particles are used
for the above-described applications, usually, metal oxide
particles are used as core particles and the surface of the
particles is coated by a shell made of a metal oxide such as
silicon oxide (silica), and then used as core-shell particles.
[0008] Further, it has been known that the core particles of the
core-shell particles are dissolved to prepare hollow particles
composed of a shell made of a metal oxide such as silicon oxide
(silica). The hollow particles have a low refractive index, and
therefore are used as a material for e.g. antireflection
coatings.
[0009] As a method for producing the core-shell particles and
hollow particles, a method comprising the following steps is known
(Patent Document 1).
[0010] Patent Document 1 discloses "a step of reacting a silicon
oxide precursor at a pH higher than 8 in a dispersion of zinc oxide
particles constituting core particles to form a shell made of
silicon oxide on the surface of zinc oxide particles, thereby to
obtain a dispersion containing core-shell particles". Further,
Patent Document 1 discloses "a step of mixing a dispersion
containing core-shell particles with an acidic cation exchange
resin to bring them into contact with each other and dissolving the
zinc oxide particles at a pH within a range of from 2 to 8 to
obtain a dispersion of hollow particles composed of the shell".
[0011] However, the above methods require a long period of time for
production of the core-shell particles, since formation of the
shell is conducted at room temperature. Further, if heating is
conducted to increase the reaction rate of the silicon oxide
precursor, the reaction of the silicon oxide precursor proceeds
also at other than the surface of the core particles to form
particles composed solely of the silicon oxide precursor. Here,
formation of particles composed solely of the silicon oxide
precursor at other than the surface of the core particles is
referred to as deposition. Further, if such deposition proceeds,
the dispersion will be gelled or the solid content will precipitate
without being dispersed in a dispersion medium.
PRIOR ART DOCUMENT
Patent Document
[0012] Patent Document 1: JP-A-2006-335605
DISCLOSURE OF THE INVENTION
Object to be Accomplished by The Invention
[0013] The present invention is to provide a method whereby
core-shell particles and hollow particles can be produced while
suppressing formation of a gel or particles made of a shell-forming
material; core-shell particles and a coating composition wherein a
shell thickness is strictly controlled; and an article having a
coating film having a high antireflection effect.
Means to Accomplish the Object
[0014] The method for producing the core-shell particles of the
present invention is characterized in that it comprises irradiating
a liquid containing core particles made of a material having a
dielectric constant of at least 10 and a metal oxide precursor with
a microwave to form a shell made of a metal oxide on the surface of
the core particles.
[0015] The core particles are preferably zinc oxide particles,
titanium oxide particles, ITO particles or manganese-doped zinc
sulfide.
[0016] The metal oxide precursor is preferably an alkoxysilane.
[0017] The core-shell particles of the present invention are ones
which are prepared by the method for producing core-shell particles
of the present invention.
[0018] The method for producing hollow particles of the present
invention is characterized in that it comprises dissolving or
decomposing the core particles of the core-shell particles prepared
by the method for producing core-shell particles of the present
invention.
[0019] The core particles are preferably zinc oxide particles.
[0020] The metal oxide precursor is preferably an alkoxysilane.
[0021] The coating composition of the present invention is
characterized in that it comprises the hollow particles prepared by
the method for producing hollow particles of the present invention
and a dispersion medium.
[0022] The article of the present invention is an article
comprising a substrate and a coating film made of the coating
composition of the present invention.
EFFECTS OF THE INVENTION
[0023] By the method for producing core-shell particles of the
present invention, it is possible to produce core-shell particles
while suppressing formation a gel or particles made of a
shell-forming material.
[0024] The core-shell particles of the present invention have a low
content of particles made of a shell-forming material and a gel,
whereby the shell thickness can be strictly controlled.
[0025] By the method for producing hollow particles of the present
invention, it is possible to produce hollow particles while
suppressing formation of a gel or particles made of a shell-forming
material.
[0026] The coating composition of the present invention have a low
content of particles made of a shell-forming material and a
gel.
[0027] The article of the present invention has a coating film
having a high antireflection effect.
BEST MODE FOR CARRYING OUT THE INVENTION
Method for Producing Core-Shell Particles
[0028] The method for producing core-shell particles of the present
invention comprises irradiating a liquid containing core particles
made of a material having a dielectric constant of at least 10 and
a metal oxide precursor with a microwave to form a shell made of a
metal oxide on the surface of the core particles.
[0029] Specifically, a method comprising the following steps may be
mentioned.
[0030] (a) A step of adding a metal oxide precursor, water as
required, an organic solvent, an alkali or acid, other additive
compounds, etc. to a dispersion of core particles wherein core
particles are dispersed in a dispersion medium to prepare a raw
material liquid.
[0031] (b) A step of heating the raw material liquid by irradiating
the raw material liquid with a microwave, and hydrolyzing the metal
oxide precursor by using the alkali or acid to deposit a metal
oxide on the surface of the core particles, to form a shell,
thereby to obtain a dispersion of the core-shell particles.
[0032] (c) A step of removing the dispersion medium from the
dispersion of core-shell particles to recover the core-shell
particles, as the case requires.
Step (a):
[0033] The dielectric constant of the material for core particles
is at least 10, preferably from 10 to 200, more preferably from 15
to 100. When the dielectric constant of the material for core
particles is at least 10, adsorption of the microwave tends to be
easy, whereby it becomes possible to heat core particles
selectively and to a high temperature by the microwave.
[0034] The electric power which is converted into heat inside of
the dielectric material at the time of irradiation with the
microwave is obtained by the following formula.
P=2.pi.fE.sup.2.di-elect cons. tan .delta.
(P: electric power, f: frequency, E: magnitude of electric field,
.di-elect cons.: dielectric constant, tan .delta.: dielectric loss
tangent)
[0035] Accordingly, the amount of generated heat is determined by
multiplication of the dielectric constant and the dielectric loss
tangent, and therefore a material having a large dielectric loss
tangent and dielectric constant tends to be easily heated. The
dielectric loss tangent is preferably from 0.001 to 1, more
preferably from 0.01 to 1.
[0036] The dielectric constant and the dielectric loss tangent can
be calculated based on values of reflection coefficient and phase
which are measured after impressing an electric field to a test
sample by a bridge circuit, by using a network analyzer.
[0037] The material for the core particles may be a material having
a dielectric constant of at least 10.
[0038] The material having a dielectric constant of at least 10
may, for example, be zinc oxide, titanium oxide, ITO, aluminum
oxide, zirconium oxide, zinc sulfide, gallium arsenide, indium
phosphide, copper aluminum disulfide, copper gallium disulfide,
copper indium disulfide, copper indium diselenide, silver indium
diselenide, yttria, yttrium vanadate, iron oxide, cadmium oxide,
copper oxide, bismuth oxide, tungsten oxide, cerium oxide, tin
oxide, gold, silver, copper, platinum, palladium, ruthenium,
ferroplatinum or carbon.
[0039] The core particles are preferably zinc oxide particles or
titanium oxide particles in view of their excellent ultraviolet
shielding properties, preferably ITO particles in view of their
excellent infrared shielding properties, and preferably
manganese-doped zinc sulfide particles in view of their excellent
photoluminescence properties.
[0040] The shape of the core particles is not particularly limited,
and a sphere-shape, an angular shape, a needle-shape, a
sheet-shape, a chain-shape, a fiber-shape or a hollow-shape may be
used.
[0041] The average agglomerated particle size (diameter) of the
core particles in the dispersion is preferably from 1 to 1,000 nm,
more preferably from 1 to 300 nm. When the average agglomerated
particle size of the core particles is at least 1 nm, the surface
area per mass of the core particles does not increase too much,
whereby the amount of a metal oxide required for coating will be
suppressed. When the average agglomerated particle size of the core
particles is at most 1,000 nm, dispersibility in the dispersion
medium becomes good.
[0042] The agglomerated particle size of the core particles in a
dispersion is measured by a dynamic light scattering method.
[0043] The concentration of the core particles is preferably from
0.1 to 40 mass %, more preferably from 0.5 to 20 mass %, in the
dispersion (100 mass %) of the core particles. When the
concentration of the core particles is at least 0.5 mass %,
production efficiency of the core-shell particles becomes good.
When the concentration of the core particles is at most 20 mass %,
agglomeration of the core particles tends to hardly occur.
[0044] The dispersion medium may, for example, be water, an alcohol
(such as methanol, ethanol or isopropanol), a ketone (such as
acetone or methyl ethyl ketone), an ether (such as tetrahydrofuran
or 1,4-dioxane), an ester (such as ethyl acetate or methyl
acetate), a glycol ether (such as ethylene glycol monoalkyl ether),
a nitrogen-containing compound (such as N,N-dimethylacetamide or
N,N-dimethylformamide) or a sulfur-containing compound (such as
dimethylsulfoxide).
[0045] The dispersion medium preferably contains water in an amount
of from 5 to 100 mass % based on 100 mass % of the dispersion
medium, since water is necessary for hydrolysis of the metal oxide
precursor.
[0046] The metal oxide may be an oxide of at least one metal
selected from the group consisting of Si, Al, Cu, Ce, Sn, Ti, Cr,
Co, Fe, Mn, Ni, Zn and Zr. The metal oxide is SiO.sub.2 when the
metal is Si, Al.sub.2O.sub.3 when the metal is Al, CuO when the
metal is Cu, CeO.sub.2 when the metal is Ce, SnO.sub.2 when the
metal is Sn, TiO.sub.2 when the metal is Ti, Cr.sub.2O.sub.3 when
the metal is Cr, CoO when the metal is Co, Fe.sub.2O.sub.3 when the
metal is Fe, MnO.sub.2 when the metal is Mn, NiO when the metal is
Ni, ZnO when the metal is Zn, or ZrO.sub.2 when the metal is
Zr.
[0047] The metal oxide precursor may, for example, be a metal
alkoxide, and is preferably an alkoxysilane in view of formation of
a compact shell.
[0048] The alkoxysilane may, for example, be tetramethoxysilane,
tetraethoxysilane (hereinafter referred to as TEOS), tetra
n-propoxysilane or tetraisopropoxysilane, and is preferably TEOS in
view of its appropriate reaction rate.
[0049] The amount of the metal oxide precursor is preferably an
amount by which the shell thickness becomes from 1 to 500 nm, more
preferably an amount by which the shell thickness becomes from 1 to
100 nm.
[0050] The amount of the metal oxide precursor (as calculated as
metal oxide) is, specifically, preferably from 0.1 to 10,000 parts
by mass based on 100 parts by mass of the core particles.
[0051] The alkali may, for example, be potassium hydroxide, sodium
hydroxide, ammonia, ammonium carbonate, ammonium hydrogencarbonate,
dimethylamine, triethylamine or aniline, and is preferably ammonia
in view of its removability by heating.
[0052] The amount of the alkali is preferably an amount by which
the pH of the raw material liquid becomes from 8.5 to 10.5, more
preferably an amount by which the pH of the raw material liquid
becomes from 9.0 to 10.0 in view of easiness in formation of a
compact shell by three-dimensional polymerization of the metal
oxide precursor.
[0053] The acid may, for example, be hydrochloric acid or nitric
acid. Further, since the zinc oxide particles are dissolved in the
acid, it is preferred to conduct hydrolysis of the metal oxide
precursor by an alkali when the zinc oxide particles are used as
the core particles.
[0054] The amount of the acid is preferably an amount by which the
pH of the raw material liquid becomes from 3.5 to 5.5.
[0055] The other additive compound may, for example, be a metal
chelate compound, an organic tin compound, a metal alkolate or a
metal fatty acid salt, and in view of the strength of the shell, it
is preferably a metal chelate compound or an organic tin compound,
particularly preferably a metal chelate compound.
[0056] The amount of the other additive compound (as calculated as
metal oxide) is preferably from 0.1 to 20 parts by mass, more
preferably from 0.2 to 8 parts by mass based on 100 parts by mass
of the amount of the metal oxide precursor (as calculated as metal
oxide).
Step (b):
[0057] The microwave is, usually, an electromagnetic wave having a
frequency of from 300 MHz to 300 GHz. Usually, a microwave having a
frequency of 2.45 GHz is used, but the microwave is by no means
restricted thereto and a frequency by which an unheated material is
efficiently heated may be selected. According to the radiowave
regulation law, a frequency band to be used for radiowave
applications other than communication, so-called ISM band, is
defined, and a microwave of e.g. 433.92 (.+-.0.87) MHz, 896 (+10)
MHz, 915 (+13) MHz, 2,375 (.+-.50) MHz, 2,450 (.+-.50) MHz, 5,800
(.+-.75) MHz or 24,125 (+125) MHz may be used.
[0058] The output power of the microwave is preferably an output
power by which the raw material liquid is heated to from 30 to
500.degree. C., more preferably an output power by which the raw
material liquid is heated to from 50 to 300.degree. C.
[0059] When the temperature of the raw material liquid is at least
30.degree. C., it is possible to form a compact shell in a short
period of time. When the temperature of the raw material liquid is
at most 500.degree. C., it is possible to suppress the amount of
metal oxide deposited at other than the surface of core
particles.
[0060] The microwave heat treatment may be a batch process, but,
for mass production, a continuous process conducted by using a flow
apparatus is more preferred. The irradiation system of the
microwave may be a single mode, but a multimode which can conduct
heating uniformly is more preferred for mass production.
[0061] The irradiation time of the microwave may be adjusted to a
period of time by which a shell having a desired thickness is
formed, depending upon the output power of the microwave
(temperature of raw material liquid), and is e.g. from 10 seconds
to 60 minutes.
Step (c):
[0062] As the method of removing the dispersion medium from the
dispersion of core-shell particles to recover the core-shell
particles, the following methods may be mentioned.
[0063] (c-1) A method of heating the dispersion of core-shell
particles to volatilize e.g. the dispersion medium.
[0064] (c-2) A method of subjecting the dispersion of core-shell
particles to solid-liquid separation, followed by drying the solid
content.
[0065] (c-3) A method of spraying the dispersion of core-shell
particles into a heated gas by using a spray dryer to volatilize
e.g. the dispersion medium (spray drying method).
[0066] (c-4) A method of cooling and depressurizing the dispersion
of core-shell particles to sublime e.g. the dispersion medium
(freeze-drying method).
[0067] In the above-mentioned method for producing core-shell
particles of the present invention, a liquid containing core
particles made of a material having a dielectric constant of at
least 10 and a metal oxide precursor, is irradiated with a
microwave, whereby it is possible to heat the core particles
selectively and to a high temperature. Therefore, even if the
temperature of the entire raw material liquid becomes a high
temperature, the core particles are heated to a higher temperature,
whereby hydrolysis of the metal oxide precursor preferentially
proceeds on the surface of the core particles to selectively
deposit a metal oxide on the surface of core particles.
Accordingly, the amount of particles made of a shell-forming
material (metal oxide) which are deposited independently at other
than the surface of the core particles can be suppressed. Further,
the shell can be formed under a high temperature condition, whereby
the shell can be formed in a short period of time.
<Core-Shell Particles>
[0068] The core-shell particles of the present invention are
core-shell particles prepared by the method for producing
core-shell particles of the present invention.
[0069] The shell thickness of the core-shell particles is
preferably from 1 to 500 nm, more preferably from 1 to 100 nm. When
the shell thickness is at least 1 nm, a photocatalytic activity of
the core particles is sufficiently suppressed, and then
degeneration or deterioration of the core particles is sufficiently
suppressed. When the shell thickness is at most 500 nm, functions
of the core particles such as ultraviolet shielding properties and
infrared shielding properties are sufficiently obtainable.
[0070] It is possible to adjust the thickness of the shell by
appropriately adjusting the amount of the metal oxide precursor,
the output power of the microwave, the irradiation time, etc. For
example, on the assumption that a shell having a desired thickness
is formed around a core particle, from the volume ratio of the core
particle to the shell, a mass ratio is calculated based on a
specific gravity of the core particle to a shell-forming material
(metal oxide), and then the charge amount of the metal oxide
precursor to the core particles is adjusted to control the shell
thickness.
[0071] The shell thickness is the average of shell thicknesses of
100 core-shell particles randomly selected by observation with a
transmission electron microscope.
[0072] The average agglomerated particle size (diameter) of the
core-shell particles is preferably from 3 to 1,000 nm, more
preferably from 3 to 300 nm. The average agglomerated particle size
of the core-shell particles is the average agglomerated particle
size of the core-shell particles in a dispersion medium and is
measured by a dynamic light scattering method.
[0073] The average primary particle size of the core-shell
particles is preferably from 3 to 500 nm, more preferably from 3 to
200 nm.
[0074] The average primary particle size (diameter) of the
core-shell particles is the average of particle sizes of 100
core-shell particles randomly selected by observation with a
transmission electron microscope.
[0075] The above-mentioned core-shell particles of the present
invention are prepared by the method for producing core-shell
particles of the present invention, whereby the amount of particles
made of the shell-forming material (metal oxide) is low, and
therefore it is possible to control the shell thickness
precisely.
<Method for Producing Hollow Particles>
[0076] The method for producing hollow particles of the present
invention is a method of dissolving or decomposing the core
particles of the core-shell particles prepared by the method for
producing core-shell particles of the present invention.
[0077] Specifically, a method comprising the following steps may be
mentioned.
[0078] (a') A step of adding a metal oxide precursor, and, as the
case requires, water, an organic solvent, an alkali or acid, and
other additive compounds, etc. to a dispersion of core particles
wherein core particles are dispersed in a dispersion medium to
prepare a raw material liquid.
[0079] (b') A step of heating the raw material liquid by
irradiating the raw material liquid with a microwave, and
hydrolyzing the metal oxide precursor by using the alkali or acid,
to deposit a metal oxide on the surface of the core particles, to
form a shell, thereby to prepare a dispersion of the core-shell
particles.
[0080] (c') A step of dissolving or decomposing core particles of
the core-shell particles contained in the dispersion to obtain a
dispersion of hollow particles made of the shell.
Step (a'):
[0081] Step (a') is the same step as step (a) of the method for
producing core-shell particles of the present invention.
[0082] The material of the core-shell particles may be one having a
dielectric constant of at least 10 and being capable of being
dissolved or decomposed in the step (c').
[0083] The core particles may, for example, be heat decomposable
organic particles (such as surfactant micells, a water soluble
organic polymer, a styrene resin or an acrylic resin), acid-soluble
inorganic particles (such as zinc oxide, sodium aluminate, calcium
carbonate or basic zinc carbonate), or photo-soluble inorganic
particles (such as zinc sulfide, cadmium sulfide or zinc oxide).
Particularly, zinc oxide particles are preferred.
Step (b'):
[0084] Step (b') is the same step as the step (b) in the method for
producing core-shell particles of the present invention.
Step (c'):
[0085] In a case where the core particles are acid-soluble
inorganic particles, the core particles can be dissolved and
removed by adding an acid.
[0086] The acid may, for example, be an inorganic acid (such as
hydrochloric acid, sulfuric acid or nitric acid), an organic acid
(such as formic acid or acetic acid) or an acidic cation exchange
resin.
[0087] In the above-mentioned method for producing hollow particles
of the present invention, the core-shell particles prepared by the
method for producing core-shell particles of the present invention
are used, whereby it is possible to suppress the amount of
particles made of the shell-forming material (metal oxide),
contained in the obtainable dispersion. Further, it is possible to
form the shell under a high temperature condition, whereby the
shell is formed in a short period of time.
<Hollow Particles>
[0088] The shell thickness of the hollow particles is preferably
from 1 to 50 nm, more preferably from 1 to 20 nm. When the shell
thickness is at least 1 nm, the strength of the hollow particles is
sufficient. When the shell thickness is at most 50 nm, it is
possible to form a coating film having a high antireflection
effect.
[0089] It is possible to adjust the shell thickness by
appropriately adjusting the amount of the metal oxide precursor,
the output power of the microwave, the irradiation time, etc.
[0090] The shell thickness is the average of shell thicknesses of
100 hollow particles randomly selected by observation with a
transmission electron microscope.
[0091] The average agglomerated particle size (diameter) of the
hollow particles is preferably from 5 to 300 nm, more preferably
from 10 to 100 nm. When the average agglomerated particle size of
the hollow particles is at least 5 nm, a sufficient air gap is
formed between adjacent hollow particles, whereby the refractive
index of the coating film becomes low, thus leading to a high
antireflection effect. When the average agglomerated particle size
of the hollow particles is at most 300 nm, scattering of light will
be suppressed, whereby a coating film with high transparency will
be obtained.
[0092] The average agglomerated particle size of the hollow
particles is the average agglomerated particle size of the hollow
particles in a dispersion medium and is measured by a dynamic light
scattering method.
[0093] The average primary particle size (diameter) of the hollow
particles is preferably from 5 to 100 nm, more preferably from 5 to
80 nm. When the average primary particle size of the hollow
particles is within these ranges, the antireflection effect of the
coating film becomes high.
[0094] The average primary particle size of the hollow particles is
the average of particle sizes of 100 hollow particles randomly
selected by observation with a transmission electron
microscope.
<Coating Composition>
[0095] The coating composition of the present invention comprises
hollow particles prepared by the method for producing hollow
particles of the present invention, a dispersion medium, and as the
case requires, a binder.
[0096] The dispersion medium may, for example, be water, an alcohol
(such as methanol, ethanol or isopropanol), a ketone (such as
acetone or methyl ethyl ketone), an ether (such as tetrahydrofuran
or 1,4-dioxane), an ester (such as ethyl acetate or methyl
acetate), a glycol ether (such as ethylene glycol monoalkyl ether),
a nitrogen-containing compound (such as N,N-dimethylacetamide or
N,N-dimethylformamide) or a sulfur-containing compound (such as
dimethylsulfoxide).
[0097] The binder may, for example, be an alkoxysilane (such as
tetramethoxysilane or TEOS), a silicic acid oligomer obtained by
hydrolyzing an alkoxysilane, a silicon compound having a silanol
group (such as silicic acid or trimethyl silanol), active silica
(such as water glass or sodium orthosilicate) or an organic polymer
(such as polyethylene glycol, a polyacrylamide derivative or
polyvinyl alcohol).
[0098] The mass ratio of the hollow particles to the binder (hollow
particles/binder) is preferably from 10/0 to 5/5, more preferably
from 9/1 to 7/3. When the hollow particles/binder (mass ratio) is
within the above range, it is possible to maintain the refractive
index of the coating film to be low and form a coating film having
a high antireflection effect.
[0099] The solid content concentration of the coating composition
of the present invention is preferably from 0.1 to 20 mass %.
[0100] The coating composition of the present invention may contain
hollow particles other than the hollow particles of the present
invention or solid fine particles within a range not to impair the
effects of the present invention.
[0101] The coating composition of the present invention may contain
known additives such as an alkaline earth metal salt such as a
chloride, nitrate, sulfate, formate or acetate of e.g. Mg, Ca, Sr
or Ba; a curing catalyst such as an inorganic acid, an organic
acid, a base, a metal chelate compound, a quaternary ammonium salt
or an organic tin compound; inorganic particles showing ultraviolet
shielding properties, infrared shielding properties or
electroconductive properties; a pigment, a dye and a
surfactant.
[0102] In the coating composition of the present invention, various
compounding agents for coating material comprising an inorganic
compound and/or an organic compound may be blended to impart one or
more functions selected from hard coating, alkali barrier,
coloring, electrical conductivity, antistatic properties,
polarization, ultraviolet shielding properties, infrared shielding
properties, antifouling properties, anti-fogging properties,
photocatalytic activity, antibacterial properties,
photoluminescence properties, battery properties, control of
refractive index, water repellency, oil repellency, removal of
fingerprint, lubricity, and the like.
[0103] To the coating composition of the present invention,
depending upon the function required for the coating film, commonly
used additives such as an antifoaming agent, a leveling agent, an
ultraviolet absorber, a viscosity modifier, an antioxidant and a
fungicide may properly be added. Further, to make the coating film
have a desired color, various pigments which are commonly used for
coating material such as titania, zirconia, white lead and red
oxide may be blended.
[0104] The above-mentioned coating composition of the present
invention contains hollow particles prepared by the method for
producing hollow particles of the present invention, whereby the
amount of solid fine particles made of a shell-forming material
(metal oxide) is low. Therefore, it is possible to form a coating
film having a low refractive index and a high antireflection
effect.
<Article>
[0105] The article of the present invention is an article having a
coating film made of the coating composition of the present
invention formed on a substrate.
[0106] The thickness of the coating film is preferably from 50 to
300 nm, more preferably from 80 to 200 nm. When the thickness of
the coating film is at least 50 nm, interference of light will
occur, whereby an antireflection effect will be developed. When the
thickness of the coating film is at most 300 nm, a film can be
formed without cracking.
[0107] The thickness of the coating film is obtained by measuring
the interface between the coated surface and the non-coated surface
by a profilometer.
[0108] The refractive index of the coating film is preferably from
1.2 to 1.4, more preferably from 1.23 to 1.35. When the refractive
index of the coating film is at least 1.2, the light reflected on
the upper film surface and the light reflected on the lower film
surface are offset by interference, whereby a coating film having a
high antireflection effect is obtained. When the refractive index
of the coating film is at most 1.4, the light reflected on the
upper film surface and the light reflected on the lower film
surface are offset by interference, whereby a coating film having a
high antireflection effect will be obtained when glass is used as
the substrate. The refractive index of the coating film is
preferably from 0.0 to 1.4%, more preferably from 0.0 to 1.0%.
[0109] The refractive index of the coating film is a refractive
index at 550 nm and is measured by a refractometer.
[0110] The coating film is formed by applying the coating
composition of the present invention to the surface of a substrate
and drying it. The coating film is preferably further heated or
baked from the viewpoint of the film strength, and is more
preferably baked in a tempering step of glass from the view point
of cost.
[0111] The material of the substrate may, for example, be glass, a
metal, an organic polymer or silicon, and the substrate may be a
substrate having any coating film preliminarily formed thereon. As
the glass, not only glass formed by float process or the like but
also patterned glass obtained by rollout process by supplying
molten glass between a roll member having irregularities imprinted
on the surface and another roll member may be used. Particularly,
glass having a coating film formed by applying and drying the
coating composition of the present invention can be preferably used
as a cover glass of solar cells. In such a case, the coating film
is preferably formed on the smooth surface (a surface with a low
degree of irregularities) of the patterned glass. The organic
polymer may, for example, be polyethylene terephthalate
(hereinafter referred to as PET), polycarbonate, polymethyl
methacrylate or triacetyl acetate.
[0112] The shape of the substrate may, for example, be a plate or a
film.
[0113] On the article of the present invention, another functional
layer (such as an adhesion-improving layer or a protective layer)
may be formed in a range not to impair the effects of the present
invention. Further, in the present invention, it is preferred that
only the coating film of the present invention is formed, in view
of productivity and durability.
[0114] On the substrate, a coating film comprising an inorganic
compound and/or an organic compound may be preliminarily formed to
impart one or more functions selected from hard coating, alkali
barrier, coloring, electrical conductivity, antistatic properties,
polarization, ultraviolet shielding properties, infrared shielding
properties, antifouling properties, anti-fogging properties,
photocatalytic activity, antibacterial properties,
photoluminescence properties, battery properties, control of
refractive index, water repellency, oil repellency, removal of
fingerprint, lubricity, and the like. Further, on the coating film
obtained by applying the coating composition of the present
invention, a functional coating film comprising an inorganic
compound and/or an organic compound may be formed to impart one or
more functions selected from hard coating, alkali barrier,
coloring, electrical conductivity, antistatic properties,
polarization, ultraviolet shielding properties, infrared shielding
properties, antifouling properties, anti-fogging properties,
photocatalytic activity, antibacterial properties,
photoluminescence properties, battery properties, control of
refractive index, water repellency, oil repellency, removal of
fingerprint, lubricity, and the like.
[0115] As the coating method, a known method such as bar coating,
die coating, gravure coating, roll coating, flow coating, spray
coating, online spray coating, ultrasonic spray coating, inkjet, or
dip coating may be mentioned. The online spray coating is a method
of spray coating on the same line for formation of the substrate,
and is capable of producing articles at a low cost and is useful,
since a step of re-heating the substrate can be omitted.
[0116] The above-mentioned article of the present invention has a
coating film made of the coating composition of the present
invention, and therefore it has a high antireflection effect.
EXAMPLES
[0117] Now, the present invention will be described in further
detail with reference to Examples and Comparative Examples, but it
should be understood that the present invention is by no means
restricted thereto.
[0118] Examples 1 to 8 are Examples of the present invention, and
Examples 9 to 14 are Comparative Examples.
(Average Agglomerated Particle Size of Core Particles)
[0119] The average agglomerated particles size of the core
particles was measured by a dynamic light scattering particle size
analyzer (Microtrac UPA, manufactured by NIKKISO, CO., LTD.).
(Dielectric Constant)
[0120] The dielectric constant of the material for core particles
was calculated based on values of reflection coefficient and phase
which were measured after impressing an electric field to a test
sample by a bridge circuit, by using a network analyzer (PNA
microwave vector network analyzer, manufactured by Agilent
Technologies Inc.).
(State of Liquid)
[0121] The state of a raw material liquid after heating was
confirmed by visual observation and a transmission electron
microscope.
[0122] Dispersion: Core-shell particles are uniformly dispersed in
a dispersion medium (confirmed by visual observation).
[0123] Deposition: Besides core-shell particles, silicon oxide
particles are deposited in a large amount (confirmed by a
transmission electron microscope).
[0124] Precipitation: A solid content is precipitated without being
dispersed in a dispersion medium (confirmed by visual
observation).
(Shell Thickness)
[0125] A dispersion of core-shell particles was diluted to 0.1 mass
% with ethanol, sampled on a collodion membrane and observed by a
transmission electron microscope, whereby 100 particles were
randomly selected and the shell thicknesses of the respective
core-shell particles were measured, whereupon the shell thicknesses
of 100 core-shell particles were averaged.
(Minimum Reflectance)
[0126] The reflectance of a coating film on a substrate at from 380
to 1,200 nm was measured by an electrophotometer (model: U-4100,
manufactured by Hitachi, Ltd.) to obtain the minimum value of the
reflectance (minimum reflectance).
Example 1
[0127] To a 200 mL pressure-resistant container made of quartz,
55.6 g of an aqueous dispersion (average agglomerated particle
size: 30 nm, solid content concentration: 20 mass %) of zinc oxide
(ZnO, dielectric constant: 18) particles, 6.9 g of TEOS (solid
content concentration as calculated as silicon oxide: 28.8 mass %)
(target shell thickness: 2 nm), 36.9 g of ethanol, and 0.6 g of 28
mass % aqueous ammonia were added to prepare a raw material liquid
having pH of 10.
[0128] The pressure-resistant container was tightly sealed, and
then the raw material liquid was irradiated with a microwave (MW)
having a maximum output power of 500 W and frequency of 2.45 GHz
for 5 minutes by using a microwave heating apparatus to hydrolyze
TEOS and deposit silicon oxide on the surface of zinc oxide
particles to form a shell, whereby 100 g of a dispersion of
core-shell particles was obtained. The temperature of the reaction
mixture during microwave irradiation was 120.degree. C. The state
of the dispersion of core-shell particles was observed. The results
are shown in Table 1.
[0129] A portion of the dispersion of core-shell particles was
sampled, and then the shell thickness was measured by a
transmission electron microscope and was found to be 2 nm i.e. the
same as the desired shell thickness. The results are shown in Table
1.
[0130] 100 g of a strongly acidic cation exchange resin (total
exchange capacity: at least 2.0 meq/mL) was added to 100 g of the
dispersion of the core-shell particles, followed by stirring for 1
hour, and after the pH became 4, the strongly acidic cation
exchange resin was removed by filtration to obtain a dispersion of
hollow particles. The dispersion was concentrated by
ultrafiltration to a solid content concentration of 20 mass %.
[0131] To a 200 mL glass container, 6 g of the dispersion (solid
content concentration: 20 mass %) of the hollow particles, 6 g of a
silicic acid oligomer solution (solid content concentration: 5 mass
%) and 88 g of ethanol were added, followed by stirring for 10
minutes to obtain a coating composition (solid content
concentration: 1.5 mass %).
[0132] The coating composition was applied to the surface of a
glass substrate (100 mm.times.100 mm, thickness 3.5 mm) wiped with
ethanol and spin-coated at a rotational speed of 200 rpm for 60
seconds for uniformalization, and baked at 650.degree. C. for 10
minutes to form a coating film having a thickness of 100 nm. The
minimum reflectance of the coating film was measured. The results
are shown in Table 1.
Example 2
[0133] 100 g of the dispersion of core-shell particles was obtained
in the same manner as in Example 1 except that the amount of the
aqueous dispersion of zinc oxide particles was changed to 62.5 g,
the amount of TEOS was changed to 3.5 g (target shell thickness: 1
nm), the amount of ethanol was changed to 33.7 g, the amount of
aqueous ammonia was changed to 0.3 g, the maximum output power of
microwave was changed to 1,000 W, and the irradiation time of
microwave was changed to 2 minutes. The temperature of the reaction
mixture during microwave irradiation was 180.degree. C. The state
of the dispersion of core-shell particles was observed. The results
are shown in Table 1.
[0134] Further, by the same operation as in Example 1, the shell
thickness was measured, and it was found to be 1 nm i.e. the same
as the desired shell thickness. The results are shown in Table
1.
[0135] Further, by the same operation as in Example 1, a dispersion
and coating composition of hollow particles were obtained, and then
a coating film was formed. The minimum reflectance of the coating
film was measured. The results are shown in Table 1.
Example 3
[0136] 100 g of a dispersion of core-shell particles was obtained
in the same manner as in Example 1 except that the output power of
microwave was changed to 100 W and the irradiation time of
microwave was changed to 60 minutes. The temperature of the
reaction mixture during microwave irradiation was 60.degree. C. The
state of the dispersion of core-shell particles was observed. The
results are shown in Table 1.
[0137] A silicic acid oligomer solution (solid content
concentration: 2 mass %) was applied to the surface of a glass
substrate (100 mm.times.100 mm, thickness 3.5 mm) wiped with
ethanol and spin-coated at a rotational speed of 200 rpm for 60
seconds for uniformalization, and dried at 200.degree. C. for 10
minutes to form a coating film having a thickness of 100 nm.
[0138] Further, by the same operation as in Example 1, the shell
thickness was measured, and it was found to be 2 nm i.e. the same
as the desired shell thickness. The results are shown in Table
1.
[0139] Further, by the same operation as in Example 1, a dispersion
and coating composition of hollow particles were obtained to form a
coating film. The minimum reflectance of the coating film was
measured. The results are shown in Table 1.
Example 4
[0140] To a 200 mL pressure-resistant container made of quartz,
45.5 g of an aqueous dispersion of zinc oxide particles (average
agglomerated particle size: 70 nm, solid content concentration: 20
mass %), 3.5 g of TEOS (solid content concentration as calculated
as silicon oxide: 28.8 mass %) (target shell thickness: 2 nm), 50.7
g of ethanol and 0.3 g of 28 mass % aqueous ammonia were added to
prepare a raw material liquid having pH of 10.
[0141] The pressure-resistant container was tightly sealed, and
then the raw material liquid was irradiated with a microwave (MW)
having a maximum output power of 1,400 W and frequency of 2.45 GHz
for 15 minutes by using a microwave heating apparatus to hydrolyze
TEOS and deposit silicon oxide on the surface of zinc oxide
particles to form a shell, whereby 100 g of a dispersion of
core-shell particles was obtained. The temperature of the reaction
mixture during microwave irradiation was 280.degree. C. The state
of the dispersion of core-shell particles was observed. The results
are shown in Table 1.
[0142] Further, by the same operation as in Example 1, the shell
thickness was measured, and it was found to be 2 nm i.e. the same
as the desired shell thickness. The results are shown in Table
1.
[0143] Further, by the same operation as in Example 1, a dispersion
and coating composition of hollow particles were obtained to form a
coating film. The minimum reflectance of the coating film was
measured. The results are shown in Table 1.
Example 5
[0144] To a 200 mL pressure-resistant container made of quartz, 50
g of an aqueous dispersion (average agglomerated particle size: 20
nm, solid content concentration: 1.0 mass %) of titanium oxide
particles (dielectric constant: 30), 1 g of TEOS (solid content
concentration as calculated as silicon oxide: 28.8 mass %) (target
shell thickness: 3 nm), 48.1 g of ethanol and 0.9 g of 28 mass %
aqueous ammonia were added to prepare a raw material liquid having
pH of 10.
[0145] The pressure-resistant container was tightly sealed, and
then the raw material liquid was irradiated with a microwave (MW)
having a maximum output power of 1,000 W and frequency of 2.45 GHz
for 5 minutes by using a microwave heating apparatus to hydrolyze
TEOS and deposit silicon oxide on the surface of titan oxide
(TiO.sub.2) particles to form a shell, whereby 100 g of a
dispersion of core-shell particles was obtained. The temperature of
the reaction mixture during microwave irradiation was 120.degree.
C. The state of the dispersion of core-shell particles was
observed. The results are shown in Table 1.
[0146] Further, by the same operation as in Example 1, the shell
thickness was measured, and it was found to be 3 nm i.e. the same
as the desired shell thickness. The results are shown in Table
1.
Example 6
[0147] To a 200 mL pressure-resistant container made of quartz,
62.5 g of an aqueous dispersion (average agglomerated particle
size: 60 nm, solid content concentration: 8 mass %) of ITO
(dielectric constant: 24) particles, 10.4 g of TEOS (solid content
concentration as calculated as silicon oxide: 28.8 mass %) (target
shell thickness: 15 nm), 26.2 g of ethanol and 0.9 g of 28 mass %
aqueous ammonia were added to prepare a raw material liquid having
pH of 10.
[0148] The pressure-resistant container was tightly sealed, and
then the raw material liquid was irradiated with a microwave (MW)
having a maximum output power of 1,000 W and frequency of 2.45 GHz
for 5 minutes by using a microwave heating apparatus to hydrolyze
TEOS and deposit silicon oxide on the surface of ITO particles to
form a shell, whereby 100 g of a dispersion of core-shell particles
was obtained. The temperature of the reaction mixture during
microwave irradiation was 120.degree. C. The state of the
dispersion of core-shell particles was observed. The results are
shown in Table 1.
[0149] Further, by the same operation as in Example 1, the shell
thickness was measured, and it was found to be 15 nm i.e. the same
as the desired shell thickness. The results are shown in Table
1.
Example 7
[0150] To a 20 L plastic container, 5,560 g of an aqueous
dispersion (average agglomerated particle size: 30 nm, solid
content concentration: 20 mass %) of zinc oxide (ZnO, dielectric
constant: 18) particles, 690 g of TEOS (solid content concentration
as calculated as silicon oxide: 28.8 mass %) (target shell
thickness: 2 nm), 3,690 g of ethanol and 60 g of 28 mass % aqueous
ammonia were added to prepare a raw material liquid having pH of
10.
[0151] The raw material liquid was introduced at a rate of 167
mL/minute to a flow microwave heating apparatus by pumping, and
then irradiated with a multimode microwave having a maximum output
power of 5 kW and frequency of 2.45 GHz to hydrolyze TEOS and
deposit silicon oxide to the surface of zinc oxide particles to
form a shell, whereby 10 kg of a dispersion of core-shell particles
was obtained. The temperature of the reaction mixture was reached
to 120.degree. C. in 3 minutes by microwave irradiation. The state
of the dispersion of core-shell particles was observed. The results
are shown in Table 1.
[0152] A portion of the dispersion of core-shell particles was
sampled, and then the shell thickness was measured by a
transmission electron microscope and was found to be 2 nm i.e. the
same as the desired shell thickness. The results are shown in Table
1.
[0153] 100 g of a strongly acidic cation exchange resin (total
exchange capacity: at least 2.0 meq/mL) was added to 100 g of the
dispersion of the core-shell particles, followed by stirring for 1
hour, and after the pH became 4, the strongly acidic cation
exchange resin was removed by filtration to obtain a dispersion of
hollow particles. The dispersion was concentrated by
ultrafiltration to a solid content concentration of 20 mass %.
[0154] To a 200 mL glass container, 6 g of the dispersion (solid
content concentration: 20 mass %) of the hollow particles, 6 g of a
silicic acid oligomer solution (solid content concentration: 5 mass
%) and 88 g of ethanol were added, followed by stirring for 10
minutes to obtain a coating composition (solid content
concentration: 1.5 mass %).
[0155] The coating composition was applied to the surface of a
glass substrate (100 mm.times.100 mm, thickness 3.5 mm) wiped with
ethanol and spin-coated at a rotational speed of 200 rpm for 60
seconds for uniformalization, baked at 650.degree. C. for 10
minutes, and then rapidly cooled (glass tempering condition) to
form a coating film having a thickness of 100 nm. The minimum
reflectance of the coating film was measured. The results are shown
in Table 1.
[0156] When the flow microwave heating apparatus was used in the
same manner, hollow particles having the same properties as
particles prepared by a small batch apparatus were obtained.
Example 8
[0157] To a 200 mL pressure-resistant container made of quartz, 50
g of an aqueous dispersion (average agglomerated particle size: 10
nm, solid content concentration: 1.0 mass %) of manganese-doped
zinc sulfide (ZnS:Mn, dielectric constant: 13) particles, 4 g of
TEOS (solid content concentration as calculated as silicon oxide:
28.8 mass %) (target shell thickness: 3 nm), 42.4 g of ethanol and
3.6 g of 28 mass % aqueous ammonia were added to prepare a raw
material liquid having pH of 10.
[0158] The pressure-resistant container was tightly sealed, and
then the raw material liquid was irradiated with a microwave (MW)
having a maximum output power of 1,000 W and frequency of 2.45 GHz
for 5 minutes by using a microwave heating apparatus to hydrolyze
TEOS and deposit silicon oxide on the surface of manganese-doped
zinc sulfide (ZnS:Mn) particles to form a shell, whereby 100 g of a
dispersion of core-shell particles was obtained. The temperature of
the reaction mixture during microwave irradiation was 120.degree.
C. The state of the dispersion of core-shell particles was
observed. The results are shown in Table 2.
[0159] Further, by the same operation as in Example 1, the shell
thickness was measured, and it was found to be 3 nm i.e. the same
as the desired shell thickness. The results are shown in Table
2.
Example 9
[0160] To a 200 mL pressure-resistant container made of quartz,
25.0 g of an aqueous dispersion of zinc oxide particles (average
agglomerated particle size: 30 nm, solid content concentration: 20
mass %), 10.4 g of TEOS (solid content concentration as calculated
as silicon oxide: 28.8 mass %) (target shell thickness: 5.5 nm),
63.7 g of ethanol and 0.9 g of 28 mass % aqueous ammonia were added
to prepare a raw material liquid having pH of 10.
[0161] The pressure-resistant container was tightly sealed, and
then the raw material liquid was heated at 120.degree. C. for 5
minutes by using oil bath (OB). However, the solid content was
precipitated without being dispersed in the dispersion medium,
whereby the dispersion of core-shell particles was not obtained.
The results are shown in Table 2.
Example 10
[0162] The operation was conducted in the same manner as in Example
7 except that heating by oil bath was conducted at 180.degree. C.
for 2 minutes. However, the solid content was precipitated without
being dispersed in the dispersion medium, whereby the dispersion of
core-shell particles was not obtained. The results are shown in
Table 2.
Example 11
[0163] 100 g of a dispersion of core-shell particles was obtained
by the same operation as in Example 7 except that heating by oil
bath was conducted at 60.degree. C. for 60 minutes. The state of
the dispersion of core-shell particles was observed. The results
are shown in Table 2. Besides core-shell particles, silicon oxide
particles were deposited in a large amount.
[0164] Further, by the same operation as in Example 1, the shell
thickness was measured, and it was found to be 1 nm i.e. remarkably
smaller than the desired shell thickness. The results are shown in
Table 2.
[0165] Further, by the same operation as in Example 1, a dispersion
and coating composition of hollow particles were obtained to form a
coating film. The minimum reflectance of the coating film was
measured. The results are shown in Table 2. The antireflection
effect of the coating film was found to be low.
Example 12
[0166] The raw material liquid was prepared in the same manner as
in Example 5.
[0167] The pressure-resistant container was tightly sealed, and
then the raw material liquid was heated at 120.degree. C. for 5
minutes by using oil bath. However, the solid content was
precipitated without being dispersed in the dispersion medium,
whereby the dispersion of core-shell particles was not obtained.
The results are shown in Table 2.
Example 13
[0168] The raw material liquid was prepared in the same manner as
in Example 6.
[0169] The pressure-resistant container was tightly sealed, and
then the raw material liquid was heated at 120.degree. C. for 5
minutes by using oil bath. However, the solid content was
precipitated without being dispersed in the dispersion medium,
whereby the dispersion of core-shell particles was not obtained.
The results are shown in Table 2.
Example 14
[0170] 100 g of a dispersion of core-shell particles was obtained
by the same operation as in Example 8 except that stirring was
conducted at 20.degree. C. for 6 hours.
[0171] The dispersion state of core-shell particles was observed.
The results are shown in Table 1. Although the dispersion state was
good, formation of a gel required a long period of time. Further,
the shell thickness was measured by the same operation as in
Example 1, and it was found to be 5.5 nm i.e. the same as the
desired shell thickness. The results are shown in Table 2.
[0172] Further, by the same operation as in Example 1, a dispersion
and coating composition of hollow particles were obtained to form a
coating film. The minimum reflectance of the coating film was
measured. The results are shown in Table 2.
TABLE-US-00001 TABLE 1 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7
Core Material ZnO ZnO ZnO ZnO TiO.sub.2 ITO ZnO particles Average
agglomerated 30 30 30 70 20 60 30 particle size (nm) Dielectric
constant 18 18 18 18 30 24 18 Shell Material TEOS TEOS TEOS TEOS
TEOS TEOS TEOS formation Heat source MW MW MW MW MW MW MW condition
Raw material liquid 120 180 60 280 120 120 120 temperature
(.degree. C.) Time (min) 5 2 60 15 5 5 5 Frequency (GHz) 2.45 2.45
2.45 2.45 2.45 2.45 2.45 Maximum output power 500 1000 100 1400
1000 1000 5000 (W) Evaluation State of liquid Dispersion Dispersion
Dispersion Dispersion Dispersion Dispersion Dispersion Average
agglomerated particle size of core-shell 60 60 60 100 50 80 70 or
hollow particles (nm) Shell thickness (nm) 2 1 2 2 3 15 2 Minimum
reflectance (%) 0.28 0.10 0.95 0.30 -- -- 0.25
TABLE-US-00002 TABLE 2 Ex. 8 Ex. 9 Ex. 10 Ex. 11 Ex. 12 Ex. 13 Ex.
14 Core Material ZnS: Mn ZnO ZnO ZnO TiO.sub.2 ITO ZnO particles
Average agglomerated 10 30 30 30 20 60 30 particle size (nm)
Dielectric constant 13 18 18 18 30 24 18 Shell Material TEOS TEOS
TEOS TEOS TEOS TEOS TEOS formation Heat source MW OB OB OB OB OB --
condition Raw material liquid 120 120 180 60 120 120 20 temperature
(.degree. C.) Time (min) 5 5 2 60 5 5 360 Frequency (GHz) 2.45 --
-- -- -- -- -- Maximum output power 1000 -- -- -- -- -- -- (W)
Evaluation State of liquid Dispersion Precipitation Precipitation
Deposition Precipitation Precipitation Dispersion Average
agglomerated 20 -- -- 50 -- -- 70 particle size of core-shell or
hollow particles (nm) Shell thickness (nm) 3 -- -- 1 -- -- 5.5
Minimum reflectance (%) -- -- -- 2.2 -- -- 0.8
[0173] By microwave heating, core-shell particles having no
precipitation and independent deposition of a shell composition was
obtained in a short period of time. The reason for this was
considered that core particles were selectively heated by microwave
irradiation, whereby the shell formation reaction proceeded only at
the surface of core particles. By application of microwave heating,
it becomes possible to control the shell thickness to a
predetermined level. Therefore, it is useful in view of obtaining
core-shell particles having a thick shell and a high core particle
protection effect, and hollow particles having a thin shell
thickness and a low refractive index.
INDUSTRIAL APPLICABILITY
[0174] The core-shell particles obtained by the production method
of the present invention are useful as resin fillers, cosmetics,
coatings for glass, etc.
[0175] The hollow particles obtained by the production method of
the present invention are useful as a material for antireflection
coatings, etc.
[0176] The article having the coating film comprising the coating
composition of the present invention formed thereon is useful as
e.g. a transparent component for vehicles (such as a headlight
cover, a side mirror, a front transparent substrate, a side
transparent substrate or a rear transparent substrate), a
transparent component for vehicles (such as an instrument panel
surface), a meter, a building window, a show window, a display
(such as a notebook computer, a monitor, LCD, PDP, ELD, CRT or
PDA), a LCD color filter, a substrate for a touch panel, a pickup
lens, an optical lens, a lens for glasses, a camera component, a
video component, a cover substrate for CCD, an optical fiber edge
face, a projector component, a copying machine component, a
transparent substrate for solar cells, a screen for a cell-phone, a
backlight unit component (such as a light guide plate or a
cold-cathode tube), a backlight unit component liquid crystal
brightness-improving film (such as a prism or a semi-transmissive
film), a liquid crystal brightness-improving film, an organic EL
light emitting device component, an inorganic EL light emitting
device component, a phosphor light emitting device component, an
optical filter, an edge face of an optical component, an
illuminating lamp, a cover for a light filament, an amplified laser
light source, an antireflection film, a polarizing film, an
agricultural film, etc.
[0177] The entire disclosure of Japanese Patent Application No.
2008-145490 filed on Jun. 3, 2008 including specification, claims
and summary is incorporated herein by reference in its
entirety.
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